Abstract—The most advantageous characteristic of the materials made of synthetic polymers, such as their resistance to biodegradation, is simultaneously the reason for their accumulation and environmental pollution. Nevertheless, some type of plastics under aerobic conditions undergo slow microbial degradation, however, there is lack of information on the anaerobic degradation of plastics. In this work, we studied the growth of anaerobic moderately thermophilic (55°C) consortiums in the presence of samples made of polypropylene (PP) and polyvinyl chloride (PVC). It was shown that the microbial biomass increased compared to the control, as well as anaerobic decomposition products (CO2, H2, and H2S) were detected, and the total weight of the plastics decreased by 4.4% (PP) and 6.5% (PVC) compared to the control. Bacterial cells adhere and form colonies and biofilms on the surface of the plastic materials. An analysis of the composition of microbial communities showed an increased number of anaerobic hydrolytics of the genus Tepidimicrobium, potential syntrophic bacteria of the genus Tepidanaerobacter, and especially sulfate-reducing bacteria (Desulfohalotomaculum). With help of differential scanning calorimetry and Fourier spectroscopy it was revealed that the decrease in the mass of plastic mainly occurred due to the hydrolysis of additives (plasticizers). The role of such microbial communities in the aquatic environment and anaerobic layers of the municipal solid waste landfills, where PP and PVC plastics can be destructed under the elevated temperatures of anaerobic conditions, is discussed.

Resistance to biodegradation, which is among the most advantageous features of synthetic polymers, is also the reason for their accumulation in the environment and therefore pollution. While some type of plastics are known to undergo slow microbial degradation under oxic conditions, the information on the anaerobic degradation of plastics is scarce. In this work, we studied the growth of anaerobic moderately thermophilic (55°C) consortia in the presence of samples made of polypropylene (PP) and polyvinyl chloride (PVC). It was shown that microbial biomass increased compared to the control, and the products of anaerobic decomposition (CO2, H2, and H2S) were detected, while the total weight of the plastics decreased by 4.4

The cultures assigned to the genus Thermoanaerobacterium according to the partial sequencing of the 16S rRNA gene were isolated on CM3 and GS2 media at 55°С from two laboratory methanogenic thermophilic cellulolytic microbial communities producing biogas from various paper substrates. Cellulolytic activity was shown for three isolates grown on solid and in liquid media with microcrystalline cellulose and filter paper as the only substrates. In order to compare the phylogenetic relations between these isolates and the reference strains of T. thermosaccharolyticum (DSM 571, M0795, and TG57), it was shown that the isolates I2 and I3 belonged to one cluster, whereas the I1 isolate formed a separate branch on the phylogenetic tree. A unique feature of isolate I2 is the formation of an insoluble yellow affinity substance (YAS), which is usually produced by certain anaerobic cellulolytic bacteria, such as Clostridium thermocellum; it is considered a binding component between the cellulase enzyme and its substrate, cellulose. Our results confirmed that cellulolytic T. thermosaccharolyticum strains predominated among cellulose-degrading bacteria within the thermophilic microbial communities converting the paper substrates into biogas. Although the type strain T. thermosaccharolyticum DSM 571 lacks cellulolytic capacity, our results are consistent with the recent data on the ability of several T. thermosaccharolyticum strains to degrade cellulose.

— The growing worldwide production of synthetic plastics leads to increased amounts of plastic pollution. Even though microbial degradation of plastics is known to be a very slow process, this capacity has been found in many bacteria, including invertebrate symbionts, and microscopic fungi. Research in this field has been mostly focused on microbial degradation of polyethylene, polystyrene, and polyethylene terephthalate (PET). Quite an arsenal of different methods is available today for detecting processes of plastic degradation and measuring their rates. Given the lack of generally accepted protocols, it is difficult to compare results presented by different authors. PET degradation by recombinant hydrolases from thermophilic actinobacteria happens to be the most efficient among the currently known plastic degradation processes. Various approaches to accelerating microbial plastic degradation are also discussed.

The structure of the microbial community digesting various waste papers under the thermophilic (55 degrees C) conditions was analyzed by a multilateral approach, comprising the denaturing gradient gel electrophoresis (DGGE) and the high-throughput sequencing (HTS), supported by the light- and scanning electron microscopy (SEM). The most abundant and diverse microbial populations were observed when the office paper, corrugated carton and the waste paper mixture were used, whereas the poorest communities were detected on the magazine paper and newspaper. These results were also confirmed by the DGGE analysis. Within Bacteria, the main groups were affiliated to Firmicutes (Acetivibrio, Herbinix, Thermoanaerobacterium, Tepidanaerobacter). Bacteria, identified as Acetivibrio cellulolyticus, due to the comparative analysis within databases, belong to the genus Ruminiclostridium Methanothermobacter and Methanosarcina were among the dominant Archaea. The HTS analysis showed the high prevalence of Clostridia (Ruminiclostridium). The representatives of all the trophic groups, needed for an efficient bioconversion of the wastepaper into the biogas, were detected by HTS as well, including diverse hydrolytics and fermentative species. The presence and amount of the syntrophic acetate-oxidizing bacteria Tepidanaerobacter and Thermoanaerobacterium, and their tight association with the hydrogenotrophic methanogens, are discussed concerning the completeness and effectiveness of the bioutilization of different types of non-pretreated papers.

Four previously isolated methanogenic anaerobic consortia, which were originally cultivated on a cellulose-containing substrate (filter paper), were used as inocula for the anaerobic conversion of the biomass of Anabaena variabilis into biogas at 55°C. The cumulative methane yield in the biogas produced by the most active consortia reached 64%. However, the biotransformation was only efficient in the course of the single inoculation and pretreatment of the cyanobacterial biomass by its concentration and freeze-thawing. The DGGE analysis of the structure of the selected microbial consortia, cultivated on the filter paper, revealed qualitative variations in the biodiversity of predominant Bacteria, showing differences in band number and intensity. The composition of methanogenic Archaea in these consortia was similar, with the presence of the genera Methanoculleus and Methanosarcina. The efficiency of the microbial consortia selection, and the role of the various microbial trophic groups in bioconversion of the substrates, such as cellulose and the biomass of phototrophic microorganisms are discussed.

The ability of micromycetes Trichoderma viride and Aspergillus terreus to decompose the cellulosecontaining substrates was studied. Office paper and cardboard, as well as a paper mixture, were found to be the most hydrolyzable. The cellulolytic activity of T. viride was 2–3 times higher than that of A. terreus; the highest values of 0.80 and 0.73 U/mL were obtained from office paper and the mixture of different types of paper, respectively. The micromycete cultivation conditions (composition of culture medium, sucrose cosubstrate addition, seeding technique) and the conditions of the fungus biomass treatment for its subsequent bioconversion into biogas by anaerobic microbial communities were optimized. It was shown that pretreatment improves the efficiency of biogas production from lignocellulosic materials when inoculated with microbial community of cattle manure. After pretreatment of the Jerusalem artichoke phytomass (stems and leaves) and its subsequent bioconversion into biogas by methanogenic community, the biogas yield was increased by1.5 times.

Several anaerobic microbial communities that produce biogas from cellulose were isolated and examined from 24 different natural and anthropogenic sources. The most active methane producers have been selected under thermophilic conditions (+55°C). In order to optimize the cultivation conditions for better growth and development of both cellulosolitics and methanogens, the modified medium has been developed. The most stable microbial consortia maintained their activities in biogas formation for at least 5 passages. The composition of biogas has been studied by using gas chromatography. In average, the percentage of methane in produced biogas reached 60%. Microscopy studies of anaerobic microbial communities revealed the presence of morphologically different cells that varied as community stabilized.

The associated culture of kefir grains was analyzed by molecular methods for determination of the functional activity of microbial isolates and molecular genetic techniques for their identification. A combination of 16S rRNA analysis and denaturing gradient gel electrophoresis was used to determine the microbial profile of kefir grains and to reveal lactic acid bacteria of two physiological groups, differing in their ability to use lactose for lactic acid fermentation. The role of inducible β-galactosidase of lactic acid bacteria for the functional stability of the microbial community was shown in the study of the functional activity and microbial profile of the kefir grains after long-time cultivation (over 4 years) on lactose-free milk. The results obtained improve our understanding of the possible trophic interactions in such microbial communities and may be used to develop the algorithm for experimental production of a stably associated culture of kefir grains.

Several active microbial communities that form biogas via decomposition of cellulose and domestic food waste (DFW) were identified among 24 samples isolated from different natural and anthropogenic sources. The methane yield was 190–260 ml CH4/g from microbial communities grown on cellulose substrates, office paper, and cardboard at 37°C without preprocessing. Under mesophilic conditions, bioconversion of paper waste yields biogas with a methane content from 47 to 63%; however, the rate of biogas production was 1.5–2.0 times lower than under thermophilic conditions. When microbial communities were grown on DFW under thermophilic conditions, the most stable and effective of them produced 230–353 ml CH4/g, and the methane content in biogas was 54–58%. These results demonstrates the significance of our studies for the development of a technology for the biotransformation of paper waste into biogas and for the need of selection of microbial communities to improve the efficiency of the process.